Microengineered optical scanner

Abstract

A microengineered optical scanner based on a moving cantilevered dielectric waveguide is described. The waveguide is excited into resonant mechanical motion by a drive located at its root. Stress sensors detect the bending of the waveguide, allowing closed loop control of the motion. A moving image of the light emitted from the moving tip of the waveguide is created by a lens. The moving image acts as a scan line. Light back-scattered from a rough surface placed at the image plane is collected back into the waveguide by confocal imaging. The light collected in the cladding of the waveguide has higher numerical aperture than the light collected in the core. The cladding light is detected by a mode-stripping detector. Techniques for combining a cantilevered waveguide, a drive, motion sensors and a mode-stripping detector using microelectromechanical systems (MEMS) technology are described.

1 . An optical reading device having a light source, a movable optical waveguide, an actuator, a detector, and wherein the actuator and detector are integrally formed in a substrate, the movement of the waveguide being effected by action of the actuator thereon, and wherein the detector provides a confocal detection system adapted to effect a detection of light backscattered into cladding of the waveguide.  
   
   
       2 . The device as claimed in  claim 1  further including at least one motion sensor such that any movement of the waveguide is detectable by the motion sensors.  
   
   
       3 . The device as claimed in claim wherein the optical waveguide is formed as an integrated channel guide formed in dielectric materials and surrounded by a cladding of restricted lateral dimensions.  
   
   
       4 . The device as claimed in  claim 1  wherein the waveguide may be externally attached or coupled to the device.  
   
   
       5 . The device as claimed in claim wherein the optical waveguide is single-moded and polarization-preserving.  
   
   
       6 . The device as claimed in claim wherein the source is polarized and arranged to excite a single polarization mode of the waveguide.  
   
   
       7 . The device as claimed in claim wherein the optical waveguide is positioned on a suspended cantilever above a substrate.  
   
   
       8 . The device as claimed in  claim 7  wherein the waveguide is supported by a mechanical layer along its entire length.  
   
   
       9 . The device as claimed in  claim 7  wherein the waveguide has a root and is supported only near its root by a mechanical layer.  
   
   
       10 . The device as claimed in claim wherein the actuator and detector are integrally formed in a silicon based layer.  
   
   
       11 . The device as claimed in  claim 10  wherein the detector is constructed in the silicon layer as a p-n junction or p-i-n junction photodiode.  
   
   
       12 . The device as claimed in claim wherein the detector is placed beneath the waveguide to detect cladding modes present in the waveguide.  
   
   
       13 . The device as claimed in  claim 7  wherein the detector is a photodetector and is placed or formed at the tip of the cantilever.  
   
   
       14 . The device as claimed in  claim 7  wherein the photodetector is placed near the root of the cantilever.  
   
   
       15 . The device as claimed in  claim 7  wherein the actuator is placed near the root of the cantilever.  
   
   
       16 . The device as claimed in  claim 15  wherein the actuator is constructed as an electrothermal or electrostatic drive.  
   
   
       17 . The device as claimed in  claim 16  wherein the actuator is an electrothermal shape bimorph actuator.  
   
   
       18 . The device as claimed in  claim 17  wherein the waveguide is placed over a cold arm of the electrothermal shape bimorph actuator.  
   
   
       19 . The device as claimed in  claim 16  wherein the electrothermal shape bimorph actuator has dual hot arms.  
   
   
       20 . The device as claimed in  claim 18  wherein electrical current in the cold arm is monitored and suppressed using an active feedback circuit.  
   
   
       21 . The device as claimed in  claim 17  wherein the motion sensors are placed near the root of the cold arm and the root of the cantilever.  
   
   
       22 . The device as claimed in  claim 21  wherein the motion sensors are constructed as pairs of piezo-resistors, arranged to detect differential strain caused by bending of the structure and connected to a differential readout circuit.  
   
   
       23 . An optical reading system comprising a device having at least one of the following components: 
 a) a cantilevered single-mode optical waveguide suitable for transmitting light onto a target thereby illuminating the target and adapted to effect a reception of the back-scattered signal from the target into the cladding of the waveguide,    b) an actuator capable of achieving large in-plane displacement,    c) motion sensors capable of providing the necessary signals for closed loop control of the scan amplitude,    d) a cladding mode detector capable of implementing a confocal detection system so as to effect a detection of the light backscattered into the cladding of the waveguide,    e) a lens, which may be formed in the wall of the device package, the device being coupled to a laser source, which may be hybridised or integrally formed with the device of the present invention or linked thereto by a section of optical fibre so as to provide the incident light to the waveguide.    
   
   
       24 . The system as claimed in  claim 23  wherein the elements a) through e) are all fabricated in silicon-based materials using a compatible process.  
   
   
       25 . A method of forming an optical reader comprising the steps of: 
 a) forming a detector in a substrate,    b) forming an actuatable cantilever also in the substrate,    c) coupling a waveguide to the cantilever, and    wherein the cantilever and detector are integrally formed in the substrate, the waveguide being adapted to transmit light onto a target and receive light backscattered from the target, the light received back into the waveguide being detectable using the detector.